1. Field of Invention
The present invention relates to a belt tension adjustment apparatus. More particularly, the present invention relates to an apparatus for adjusting the tension of a transmission belt inside an optical scanner.
2. Description of Related Art
Due to the immense popularity of home computer products, image capture, processing and modification has become a favorite pastime for people. Since an image of whatever content must be captured and fed to a computer, a scanner has become an indispensable peripheral device of the computer. Documents, journals, texts and pictures are now routinely captured by a scanner and transmitted to a personal computer for further treatment. Among the scanners, the platform scanner is the common type. In a platform scanner, a scanning module capable of shuttling back and forth to scan a document on a transparent platform is installed underneath the transparent platform. The scanning module is externally driven by a transmission system that often includes a servo-controlled motor, a set of gear wheels and a belt. Before scanning a document, the document is placed on the transparent platform and then a cover panel is lowered onto the document so that the document is pressed firmly against the transparent panel.
FIG. 1 is a schematic cross-sectional side view of a conventional optical scanner. As shown in FIG. 1, the optical scanner includes a main body casing 100, a scanning module 800, a transmission system 500, a transmission belt 700, two belt wheels 720 and a cover panel 200. The main body casing 100 has a transparent panel 400 over the top. The scanning module 800, the transmission system 500, the transmission belt 700 and the two belt wheels 720 are all enclosed within the main body casing 100. The transmission belt 700 wraps around the pair of belt wheels 720. One belt wheel 720 is linked to and driven by the transmission system 500. The belt wheel 720 in turn drives the transmission belt 700 in such a way that the scanning module 800 attached to the belt 700 reciprocates forward and backward inside the main body casing 100 underneath the transparent panel 400. Before scanning a document 300, the document 300 is horizontally placed over the transparent panel 400 and then the cover panel 200 is lowered onto the document 300. The transmission system 500 includes an electric motor 520 and a set of gear wheels 540. Power is fed to the electric motor 520 to rotate the set of gear wheels. Once the gear wheels are driven, the belt wheel 720, the transmission belt 700 and the scanning module 800 attached to the transmission belt are all set into motion to scan the document 300 on the transparent panel 400.
In general, a constant tension must be maintained in the transmission belt 700 that straddles around the two belt wheels 720 in order to drive the scanning module 800 along smoothly. Hence, the transmission belt 700 must be tensioned up during assembly to provide the constant tension. To adjust or conduct a routine maintenance, the tension in the belt 700 must be released before dismantling the components. The most direct method of releasing the tension in the belt 700 is to loosen up one of the belt wheels 720 and moves the component such that the distance between the pair of belt wheels 720 is shortened. However, this tension-releasing method is time-consuming especially for the repair technicians who have to unleash belt tension frequently.